Peter Ewart (May 14, 1767 - September 15, 1842) was a British engineer who was influential in developing the technologies of turbines and theories of thermodynamics.

Born to a country clergyman near Dumfries, he was one of eleven siblings. His brother Joseph Ewart became a diplomat and William, a business partner of Sir John Gladstones (sic), father of William Ewart Gladstone.

After graduating from the University of Edinburgh, he was apprenticed to millwright John Rennie. His work with water wheels led him to an association with Matthew Boulton and James Watt for whom he became agent in North West England.

In 1792, frustrated in administering the immature and, as yet, unreliable machinery, he left Boulton and Watt to establish himself in cotton spinning with Samuel Oldknow. The business failed and Ewart found a new partner in Samuel Greg, installing an innovative water wheel at Greg's Quarry Bank Mill on the River Bollin in Cheshire. As a standby, he installed a Watt steam engine.

By 1811, Ewart had abandoned the venture with Greg to concentrate on his own manufacturing business but also his scientific work. He became, along with John Dalton, a vice-president of the Manchester Literary and Philosophical Society and became active in the contemporary controversies about heat, work and energy. Motivated by a paper of John Playfair and encouraged by Dalton, in 1813 he published On the measure of moving force in which he defended the nascent ideas of the conservation of energy championed by John Smeaton. The paper was strongly to influence Dalton's pupil James Prescott Joule. A vocal advocate of the application of scientific knowledge in engineering, he was one of the founders of the Manchester Mechanics' Institute.

Ewart took up an appointment with the Admiralty in 1835 and died as the result of an accident at the Woolwich Dockyard while inspecting machinery.

Bibliography

• Ewart, P (1813) "On the measure of moving force’, Memoirs of the Literary and Philosophical Society of Manchester, 2nd ser., vol.2, pp105–258
• Henry, W. C. (1846) "A biographical note of the late Peter Ewart", Memoirs of the Literary and Philosophical Society of Manchester, 2nd ser., vol.7, pp113–36
• Hodgkinson, E. (1846) "Some account of the late Mr Ewart's paper 'On the measure of moving force’", Memoirs of the Literary and Philosophical Society of Manchester, 2nd ser., vol.7, pp137–56
• Cardwell, D. S. L. (1971) From Watt to Clausius: The Rise of Thermodynamics in the Early Industrial Age, pp82–3